E. Chavarría, Liga Agricola Industrial de la Caña de Azucar, San José, Costa Rica;
F. Subirós, Azucarera El Viejo, S. A., Guanacaste, Costa Rica;
J. Vega, Ingenio San Antonio, Chinandega, Nicaragua;
G. Ralda, Ingenio Monte Rosa S. A., El Viejo, Nicaragua;
N. C. Glynn and
J. C. Comstock, Sugarcane Field Station, ARS, USDA, Canal Point, FL; and
L. A. Castlebury, Systematic Mycology and Microbiology Laboratory, Beltsville Agricultural Research Center, ARS, USDA, Beltsville, MD
Symptoms and signs of orange rust on sugarcane (a complex hybrid of Saccharum L. species) were observed from July 2007 on cv. SP 71-5574 in Costa Rica at the Coopeagri Sugar Mill located in Pérez Zeledón, San José and on multiple cultivars (CP 72-2086, Pindar, Q 132, Q 138, SP 71-5574, and SP 79-2233) at the Providencia Sugar Mill near Muelle, San Carlos and Cutris Sugar Mill near Los Chiles during August 2007. The same symptoms and signs were observed on cv. CP 72-2086 during September 2007 in Nicaragua at Ingenio San Antonio, located near Chinandega, and Ingenio Monte Rosa near El Viejo, Nicaragua. Disease symptoms and uredinia appeared different from brown rust caused by Puccinia melanocephala, and brown rust usually does not occur on these cultivars. Uredinia and urediniospores were similar to those described for orange rust (1,2). Cvs. SP 71-5574 and SP 79-2233 are susceptible and cv. CP 72-2086 is moderately susceptible to orange rust in Costa Rica and cvs. ISACP 00-1075, ISA 00-1000, and CP 72-2086 are moderately susceptible in Nicaragua. Samples from both locations (Costa Rica BPI No. 878816 and Nicaragua BPI No. 878817) examined at the USDA-ARS Mycology and Microbiology Laboratory in Beltsville, MD showed morphological characteristics consistent with those of P. kuehnii. Analysis of ITS1, 5.8S, and ITS2 rDNA sequences of the rust infecting cv. CP 72-2086 (GenBank Accession No. FJ532477) from Costa Rica and cv. ISA 00-1000 from Nicaragua (GenBank Accession No. FJ532476) confirmed the identity as P. kuehnii, the causal agent of sugarcane orange rust. Beside the cultivars already mentioned, orange rust also was confirmed on cvs. RB 73-9735 and CPCL 02-2130 in Costa Rica. To our knowledge, this is the first report of orange rust of sugarcane in Costa Rica and Nicaragua and the third confirmation of the disease in the Western Hemisphere and Caribbean Basin.
References: (1) J. C. Comstock et al. Plant Dis. 92:175, 2008. (2) W. Ovalle et al. Plant Dis. 92:973, 2008.